JPS6354480B2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The disclosed technology is applicable to arc welding of carbon steel, etc.
It belongs to the technical field of controlling the cooling rate to reduce the hardness of the welded part in the arc welding process.

Therefore, in arc welding in which a high carbon-containing ferrous material such as carbon steel or iron casting is used as a base material to be welded, the part to be welded is joined by first-stage basic arc welding, and then joined. This invention relates to an arc welding method in which a bead is formed and welding is controlled,
In particular, when forming a bead, the bead is made so that the average stress acts on the arc welding bead part below a set ratio of the average stress due to the load applied during use.
In addition, the cooling rate of the arc welding bead, or that of the subsequent bead, is controlled to be below the critical cooling rate, thereby reducing the hardness during the arc welding process. This invention relates to an arc welding method that is performed in a short period of 3 to 45 seconds.

<Prior Art> As is well known, arc welding for high carbon-containing ferrous materials, such as carbon steel and iron castings, has been widely adopted due to its various merits.

<Problems to be Solved by the Invention> Therefore, when the heat input during welding becomes small depending on the welding conditions during arc welding of materials containing high carbon content, the molten metal and the surrounding vicinity It has been found that the cooling rate of the heat-affected zone increases, resulting in relatively rapid cooling, resulting in increased hardness and deterioration of mechanical properties such as ductility.

To deal with this, the welded part is preheated using a gas burner, furnace, etc. before arc welding, or heat treatment is performed after welding to reduce the cooling rate, but basically heating is performed separately from the arc welding equipment. Device,
It requires a heating means, which has the disadvantage of requiring a large number of man-hours and poor workability. It also has the disadvantage of high equipment costs and high costs. In addition, it is extremely difficult to control the interval between heating and welding. It was hot.

<Objective of the Invention> The object of the present invention is to solve the problem of suppressing the hardness of welded molten metal parts during arc welding of high carbon-containing ferrous material workpieces, based on the above-mentioned prior art. It is an object of the present invention to provide an excellent arc welding method that is useful for the application field of joining technology in the machine manufacturing industry by adjusting the cooling rate when performing arc welding on the joint portion of base materials to be welded.

<Means/effects for solving the problems> In order to solve the above-mentioned problems, the structure of the present invention, which is based on the above-mentioned claims, is to solve the above-mentioned problems. When performing arc welding, perform arc welding on a predetermined joint to form a first stage weld bead, and place the weld bead entirely or partially overlapping the weld bead, or , a second stage weld bead is formed at a nearby location within a short period of 3 to 45 seconds after the first stage weld bead is formed by arc welding, and depending on the setting conditions, the first stage weld bead or the subsequent stage weld bead is formed by arc welding. The cooling rate of the second stage weld bead should be at least below the critical cooling rate of the former, and the stress should be 1/3 or less of the average stress due to the load acting on the molten part during use. The cooling rate of the weld bead is adjusted and controlled by forming the second stage weld bead at a predetermined time after the first stage weld bead is formed. This technology has taken technical measures to make it possible to reduce the hardness of the arc welded part during the arc welding process.

<Example> Next, an example of the present invention will be described below with reference to the drawings.

The embodiment shown in FIG. 1 is a normal butt welding mode, in which a carbon steel material 1 is connected to another carbon steel material 2.
Using this as a base material to be welded, welding is first performed on the joint 3 using a well-known arc welding means to form a first stage weld bead 4.

Thus, the first stage weld bead 4 by itself sufficiently joins the base materials 1 and 2 to be welded together by cooling and hardening at a set rate.

However, as mentioned above, if the welding heat input is relatively small compared to the heat capacity of the base materials 1 and 2 to be welded, the cooling rate will exceed the critical cooling rate, resulting in a kind of rapid cooling state and the hardness will increase. , the mechanical properties will deteriorate as described above.

Therefore, after arc welding, the first stage weld bead 4
Immediately after the formation of, for example, about 3 to 45 seconds later, a second stage bead 5 is attached at a position separated by a set distance l from the center of the first stage weld bead 4, and is formed by arc welding. .

Regarding the subsequent formation of the second stage weld bead 5, although it does not directly reinforce the joint strength of the first stage weld bead 4, the cooling rate is suppressed to form the first stage weld bead 5. This provides the function of reducing the hardness of the weld bead 4.

In that case, the design conditions are such that the cooling rate of the welded part of the first stage weld bead 4 is below the critical cooling rate for hardness generation.
The position and size of the weld bead 4 of the first stage weld bead 4 are selected according to the shape of the molten solidified part, and its thickness, that is, the amount of protrusion ^A0 from the base material 1 to be welded, is The thickness corresponds to a set ratio of the average stress due to the load acting during use, for example, 1/5 or less, and the protrusion amount is set to 1/3 of the thickness T of the base material 1 to be welded. Select and decide on, etc.

By doing this, the strength is not exceeded by the second stage bead 5, and the cooling rate is controlled to a predetermined value to perform slow cooling and reduce the hardness.

Compared to the above embodiment, the embodiment shown in FIG.
The weld bead 5 of the stage is partially overlapped with the weld bead 4 of the first stage by arc welding, and the weld bead 5 of the second stage is laterally joined to the weld bead 4 of the first stage. The embodiment shown in FIG. 3 is an embodiment in which a second stage weld bead 5 is superimposed on a first stage weld bead 4 of arc welding.

Also in the above two embodiments, the size is such that the cooling rate can be controlled below the critical cooling rate including the first stage weld bead 4 or the second stage weld bead 5 by arc welding, Similarly, the protrusion amount A ⁰ is set to 1/3 of the plate thickness T of the base material 1 to be welded so that the stress is about 1/5 of the average stress of the load that acts on the weld beads 4 and 5 during use. arc welding.

Also in the above two embodiments, by forming the second stage weld bead after arc welding under the design conditions,
The molten part of the weld is gradually cooled to reduce its hardness.

The embodiment shown in FIG. 4 is a modified version of the embodiment shown in FIG. The protrusion amount A ⁰ is set to 1/3 of the plate thickness T of the base material 2' to be welded, and the second stage weld bead 5' is formed immediately after 3 seconds from the completion of arc welding. It is.

The embodiment shown in FIG. 5 is a modification of the embodiment shown in FIG. The amount of protrusion ^A0 of the second stage weld bead 5' above the first stage weld bead 4' is also the same as the plate thickness T of the base material 2 to be welded. The overhang amount, size, and shape are designed so that the overhang amount corresponds to an average stress of 1/5 of the average stress of the applied load when both are used, and
The cooling rate of the first stage weld bead 4' is designed to be below its critical cooling rate, thereby suppressing hardness formation and lowering.

The design of the cooling rate adjustment control by the second stage weld beads 5, 5' with respect to the critical cooling rate of the first stage weld beads 4, 4' in arc welding in each of the above embodiments is shown in FIG. As shown in the CCT curve of JIS S40C, it is sufficient if the cooling rate is effectively located on the right side of the curve B of H _RC 40 with respect to the critical cooling curve A.

The timing to start welding the second-stage weld beads 5, 5' may be immediately after the formation of the first-stage weld beads 4, 4', but the timing may be determined as appropriate, for example, between 3 seconds and 45 seconds. All you have to do is choose.

According to experiments based on the above-mentioned embodiments, in arc welding of rear suspension arms of automobiles, the maximum hardness of the weld fusion zone by one-pass welding based on conventional technology is H _V 600 to 700, whereas According to this invention, the maximum hardness could be lowered to about H _V 350.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments, and various embodiments may be adopted, such as installing a plurality of second-stage weld beads for a first-stage weld bead formed by arc welding. It is possible.

As described above, regarding the cooling rate adjustment control function of the weld bead in the latter stage, it is possible to adopt appropriate design changes in size, position, and timing depending on the selection of the base material to be welded.

<Effects of the Invention> As described above, according to the present invention, in the arc welding method used for joining a pair of base materials to be welded, after performing arc welding on the joint part, the first arc welding process is performed.
Proximity within a predetermined range from the center of the weld bead of the stage,
Alternatively, the second stage weld bead is formed so that the subsequent weld bead is partially polymerized or completely polymerized, and the second stage weld bead is the first stage of the load applied to the material after welding. one stage weld bead, or
The first welding bead is designed so that an average stress of 1/3 or less of the average stress due to the load during use, including the second stage weld bead, acts, and the cooling rate is less than the critical cooling rate of the main bead. The second stage weld bead is formed at a size, position, and time determined by three conditions: immediately after arc welding for stage weld bead formation, it is performed at a short time of 3 to 45 seconds. This makes it possible to reliably control the rapid cooling of the weld bead during welding with only a two-pass arc welding process, to slowly cool the weld bead within the critical cooling rate, and thus to reduce the hardness.
An excellent effect is achieved in that the bonding strength of the materials can be prevented from decreasing.

Therefore, there is no need to generate heat using gas burners, furnaces, etc. as in the past, and the work is simple and does not require special facilities. There are significant benefits in improving the quality of the product.

Furthermore, if the welding base material is the same and the welding conditions are the same, the work can be repeated to the same degree based on theoretical analysis and experimental data, and extremely favorable results in terms of product accuracy can be obtained.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention. Figures 1, 2, and 3 are cross-sectional views of each embodiment of flat plate arc welding, and Figures 4 and 5 are cross-sectional views of each embodiment of arc welding of blocks and plates. FIG. 6 is a graph of one aspect of the cooling rate. 1, 2, 1', 2'... base metal to be welded, 4, 4'... first stage weld bead, 5, 5'... second stage weld bead.

Claims (1)

[Claims] 1. In an arc welding method in which a pair of base metals to be welded is arc welded and then another weld bead is formed in response to the weld bead formed by the arc welding, a further subsequent step after the above arc welding is performed. When forming a weld bead, the cooling rate related to the hardening of each weld bead by forming the first stage weld bead by the arc welding and the subsequent second stage weld bead. The cooling rate of the first stage weld bead is below the critical cooling rate, and the average stress due to the load applied to the first stage weld bead and the subsequent second stage weld bead due to the preceding arc welding during use of the latter. After forming the first stage weld bead by arc welding, the size of the subsequent second stage weld bead is determined so that the size is 1/3 or less of that of the former.
The cooling rate of the welded part was controlled to be small by forming the second stage weld bead within a set distance from the center of the first stage weld bead within a short time of ~45 seconds. An arc welding method characterized by: